Process for the regeneration of catalysts for the treatment of hydrocarbons

ABSTRACT

A subject-matter of the present invention is a process for the regeneration of a catalyst comprising at least one metal from Group VIII and at least one metal from Group VIB which are deposited on a refractory oxide support, comprising:
         at least one first step of heat treatment of the catalyst in the presence of oxygen and at a temperature ranging from 350° C. to 550° C.;   at least one second step of deposition, at the surface of the catalyst, of one or more additive(s) of formula (I):

RELATED APPLICATIONS

This application claims priority to French patent application No. 0856884, filed Oct. 10, 2008, and U.S. provisional patent application Ser.No. 61/110,644, filed Nov. 4, 2008. The entire disclosures of each ofthe aforementioned patent applications are incorporated herein by thisreference.

BACKGROUND OF THE INVENTION

The processes for the treatment of hydrocarbons carried out inrefineries and/or petrochemistry units include a number of treatmentscarried out in the presence of hydrogen and which are intended to modifythe structure of the hydrocarbon molecules and/or to remove undesirablecompounds from the hydrocarbon fractions, such as in particularsulphur-comprising, nitrogen-containing or aromatic compounds. Mentionmay be made, as non-limiting examples, of hydrocracking, reforming orhydrogenation processes and “hydrotreating” processes, such ashydrodesulphurization, hydrodenitrogenation, hydrodearomatization orhydrodemetallization.

These processes involve specific catalysts which comprise a poroussupport based on one or more refractory inorganic oxides on which aredeposited one or more catalytically active metals comprising at leastone metal from Group VIII of the Periodic Table of the Elements,generally in combination with one or more metals from Group VIB.

During their use, these catalysts gradually become deactivated, inparticular due to the deposition of coke at their surface, that is tosay of a mixture of heavy hydrocarbons, of carbon residues and of metalimpurities.

For the sake of economy and preserving the environment, there isincreasingly a search henceforth to reuse these catalysts after theircycle of use.

“Regeneration” processes have thus been developed, which consist intreating the spent catalysts in order to restore their activity to alevel sufficient to allow them to be reemployed.

The regeneration of spent catalysts is conventionally carried out bycombusting the coke, the catalyst being heated to a high temperature inthe presence of a gas comprising oxygen. It can be carried out in situ(that is to say, directly in the unit, after shutting it down) or exsitu (that is to say, after discharging the catalyst from the unit).

However, after their first regeneration, these catalysts exhibit anactivity which is sometimes markedly inferior to their initial activityin the fresh state.

For this reason, “rejuvenation” processes have recently been developedin which the regenerated catalysts are impregnated with an organicadditive with the aim of bringing their activity back to a level asclose as possible to that of a fresh catalyst.

Thus, Patent Application WO 96/41848 describes a process for theactivation of a hydrotreating catalyst comprising an oxide of a metalfrom Group VIII and an oxide of a metal from Group VI which aredeposited on a support. According to this process, the catalyst isbrought into contact with an additive which is a compound comprising atleast 2 hydroxyl groups and from 2 to 10 carbon atoms, or a (poly)etherof such a compound, and then the catalyst is dried under conditions suchthat at least 50% of the additive remains present on the catalyst.

This process can be applied to a fresh catalyst, the activity of whichit is desired to increase, or to a spent catalyst, which has beensubjected beforehand to a regeneration step. The preferred additives areethylene glycol, diethylene glycol and polyethylene glycols.

Patent Application EP 0 882 503 describes a process for the regenerationof a spent catalyst comprising a support based on gamma-alumina and onamorphous alumina impregnated with one or more catalytically activemetals, in which:

(1) the spent catalyst is treated in order to remove carbon-baseddeposits;

(2) the support thus treated is wetted using a chelating agent in asupporting liquid;

(3) the support, thus wetted, is subjected to an ageing phase;

(4) the support is dried, so as to evaporate the supporting liquid;

(5) the support, thus dried, is calcined.

The chelating agents cited are ethylenediaminetetraacetic acid (EDTA)and its derivatives, such as, for example, N-hydroxy-EDTA anddiammonium-EDTA, tri(2-aminoethyl)amine, triethylenetetraamine,diethylenetriaminepentaacetic acid, cyclohexanediaminetetraacetic acid,ethylene glycol bis(β-amino ethyl ether) N,N′-tetraacetic acid andtetraethylenepentaamine.

Patent Application WO 01/02092 describes a process for regenerating andrejuvenating a spent additivated catalyst comprising a step ofregeneration of the catalyst by bringing it into contact with anoxygen-comprising gas at a maximum temperature of 500° C. and then astep of rejuvenation of the catalyst by bringing the latter into contactwith an organic additive, optionally followed by drying at a temperaturesuch that at least 50% of the additive remains present on the catalyst.

The regeneration temperature is preferably between 350 and 425° C. Theorganic additive employed in this process can be any compound comprisingat least one carbon atom and one hydrogen atom.

However, the methods described in the prior art exert a number ofdisadvantages and in particular they do not always make it possible toachieve a satisfactory level of activity for the recycled catalyst.

SUMMARY OF THE INVENTION

The present invention provides a process for regenerating catalystsintended for the treatment of hydrocarbons in the field in particular ofoil refining and petrochemistry. More particularly, the presentinvention provides a process intended to regenerate spent catalysts forthe hydrotreating and/or hydroconversion of hydrocarbons, in order torestore a satisfactory level of activity to them at least approachingthat of a fresh catalyst.

The present invention also provides regenerated catalysts obtained bythis process.

The present invention still further provides the use of specificadditives in order to increase the activity of these catalysts.

A goal of the present invention is to provide an improved method forregenerating spent catalysts based on metals from Groups VIII and VIBwhich makes it possible to overcome the disadvantages of the methods ofthe prior art and to obtain an at least equivalent, and even better,level of activity.

This goal is achieved by means of a process employing the combination oftwo steps, a first step of combustion of the coke under controlledtemperature conditions, followed by a second step of deposition of aspecific additive at the surface of the catalyst.

Thus, one aspect of the present invention is a process for theregeneration of a catalyst comprising at least one metal from Group VIIIand at least one metal from Group VIB which are deposited on arefractory oxide support, comprising:

-   -   at least one first step of heat treatment of the catalyst in the        presence of oxygen and at a temperature ranging from 350° C. to        550° C.;    -   at least one second step of deposition, at the surface of the        catalyst, of one or more additive(s) of formula (I):

in which:

-   -   R₁ denotes a hydrogen atom or a saturated or unsaturated, linear        or branched hydrocarbon group comprising from 1 to 30 carbon        atoms;    -   R₂ denotes a saturated or unsaturated, linear or branched        divalent hydrocarbon group comprising from 1 to 30 carbon atoms        which can optionally comprise one or more heteroatom(s) chosen        from oxygen and nitrogen atoms;    -   R₃ denotes a saturated or unsaturated, linear or branched        hydrocarbon group comprising from 1 to 30 carbon atoms.

The process according to the invention makes it possible to restore anexcellent level of activity to the catalyst which is greater than thatfound with some processes of the prior art.

In addition, the additives of formula (I) are easy to employ.

Still further, in comparison with the regeneration processes describedin the prior art, the process according to the invention has proved toexhibit the additional advantage of resulting in a presulphurization ofthe catalyst.

This is because catalysts based on metals from Groups VIII and VIB areactive in the form of metal sulphides. This is why, immediately beforethe use of the catalyst, it is known to carry out a sulphurization ofthe latter, for the purpose of activating the metal catalytic sites byconversion of the metal oxides to metal sulphides.

This sulphurization is carried out by bringing the catalyst into contactwith one or more sulphurization agents, such as, in particular, hydrogensulphide, elemental sulphur, CS₂, organic sulphur compounds, such asmercaptans, sulphides or polysulphides, or hydrocarbon fractionsnaturally comprising sulphur compounds and/or enriched in sulphurcompounds.

The process according to the invention has proved to make it possible tosimultaneously carry out, in addition to the regeneration proper of thecatalyst, a first fixing of the sulphur, this being carried out by meansof one and the same additive. This makes it possible to obtain aregenerated catalyst which exists in the presulphurized form.

Thus, the process according to the invention makes it possible tosubstantially facilitate the final sulphurization treatment carried outat the time of the use of the recycled catalyst.

DETAILED DESCRIPTION OF THE INVENTION

The process according to the present invention comprises a first step ofheat treatment of the catalyst which consists in heating the latter at atemperature ranging from 350° C. to 550° C. in the presence of oxygen.The aim of this step is to remove the coke present at the surface of thecatalyst by combustion of the coke.

Strict control of the temperature in the catalyst is advantageous duringthis step. This is because the temperature has to be sufficiently highto allow a combustion of the coke which is as complete as possible.However, it is advantageous that the temperature not exceed 550° C.,even locally, as this would have the effect of damaging the catalyst,for example by causing a deterioration in the porosity of the latter.

In one embodiment, the first step of heat treatment is carried out at atemperature of less than or equal to 530° C. and advantageously lessthan or equal to 520° C.

According to a specific embodiment of the invention, the first step ofheat treatment is carried out, in all or in part, at a temperature ofgreater than 500° C. and less than or equal to 550° C.

This specific embodiment makes it possible to more rapidly and morecompletely remove the coke and other impurities. However, this requiresprecise control of the temperature, so that the latter does not exceed,locally, 550° C.

The temperature in the catalyst can be controlled in a way known per se,for example by means of thermocouples appropriately positioned in thebody of the catalyst.

The first step is carried out in the presence of oxygen, for example bymeans of a stream of gas comprising oxygen. This gas can be composed,for example, of air, pure or mixed with additional oxygen or with aninert gas, so as to increase or reduce the oxygen content of the air.This gas can also be composed of a mixture of oxygen and of inert gas,such as nitrogen, or of other gas mixtures comprising oxygen.

The oxygen content of the gas is advantageously controlled, so as tobetter control the combustion temperature. This content can be steadyor, on the other hand, can vary over time during the first step.

The gas flow rate is also controlled, so as to control the combustion.

The first step can comprise several phases carried out at differenttemperatures and/or in the presence of variable amounts of oxygen.

The total duration of this first step generally depends on the amount ofcatalyst to be treated, on the composition of the latter, on the amountof coke present at its surface and on the operating conditions(temperature, oxygen content). This duration decreases as thetemperature increases. In certain embodiments, it is generally between0.1 and 20 hours, advantageously between 0.2 and 10 hours.

The process according to the present invention comprises a second stepduring which one or more additive(s) of formula (I) is(are) deposited atthe surface of the catalyst.

According to one embodiment, the additive or additives of formula (I)comprise(s) only one sulphur atom.

In certain embodiments, in the formula (I), R₁ denotes a hydrogen atomor a saturated or unsaturated, linear or branched hydrocarbon groupcomprising from 1 to 8 carbon atoms and advantageously from 1 to 4carbon atoms.

In certain embodiments, R₂ denotes a saturated or unsaturated, linear orbranched divalent hydrocarbon group comprising from 1 to 8 carbon atoms,advantageously from 1 to 6 carbon atoms which can be substituted by oneor more —OH, —OR, —NH₂, —NHR or —NRR′ groups, with R and R′ denotingalkyl groups comprising from 1 to 4 carbon atoms and advantageously 1 or2 carbon atoms.

In certain embodiments, R₃ denotes a saturated or unsaturated, linear orbranched hydrocarbon group comprising from 1 to 8 carbon atoms andpreferably from 1 to 4 carbon atoms.

According to a specific embodiment, in the formula (I):

-   -   R₁ denotes a hydrogen atom or an alkyl group comprising 1 or 2        carbon atoms and, preferably, R₁ denotes a hydrogen atom;    -   R₂ denotes an alkyl group comprising from 1 to 5 carbon atoms        which can be substituted by one or more —OH groups;    -   R₃ denotes an alkyl group comprising 1 or 2 carbon atoms and,        preferably, R₁ denotes a methyl group.

According to a particularly advantageous embodiment of the invention,the additive of formula (I) is 2-hydroxy-4-methylthiobutanoic acid, thatis to say that, in the formula (I): R₁ denotes a hydrogen atom, R₂denotes a —CHOH—CH₂—CH₂— group and R₃ denotes a methyl group.

This embodiment is particularly advantageous insofar as the additive iseasy to prepare and inexpensive, since this is a compound which issimilar to the amino acid methionine and which can be synthesized bysimilar routes.

In addition, this additive exhibits the additional advantage of beingcompletely soluble in water, which allows it to be employed in the formof an aqueous solution.

The additive of formula (I) is deposited at the surface of the catalystby bringing the catalyst into contact with this additive. It is possibleto proceed in several ways, for example by bringing the catalyst intocontact with the pure additive (in particular in the liquid or gasform), or with a composition comprising the additive in a carrier fluidwhich can be liquid, gaseous or supercritical. In certain embodiments,the additive of formula (I) is deposited by bringing the catalyst intocontact with a solution or suspension of the additive in a carrierliquid.

Thus, in one particularly advantageous embodiment, the catalyst isimpregnated using a solution or dispersion of the additive in anappropriate aqueous and/or organic liquid.

In another particularly advantageous embodiment of the invention, theadditive or additives of formula (I) is (are) deposited on the catalystby impregnation with one or more aqueous solution(s) of the (of these)additive(s).

Advantageously, the aqueous solution(s) employed does (do) not compriseorganic cosolvent.

It is possible to proceed by dry impregnation of the catalyst (that isto say, using a solution having a volume less than or equal to the porevolume of the catalyst), by impregnation of the catalyst in the presenceof an excess of solution or by dipping the catalyst in an excess ofsolution.

This bringing of the catalyst into contact with the additive can beinstantaneous or can last up to 20 hours. In certain embodiments, thiscontacting operation lasts approximately 2 hours, advantageouslyapproximately 1 hour. In certain embodiments, it can be carried out at apressure ranging from atmospheric pressure to 5 bar, advantageously atatmospheric pressure.

If solvent remains, it is subsequently removed, for example by heating,so as to cause it to evaporate, or by suction, or by drying using a gasstream, optionally in the presence of heating. In any case, the removalof the residual solvent, if appropriate, must be carried out so as toretain all, or at least a substantial part, of the additive deposited atthe surface of the catalyst and to prevent the additive fromdecomposing.

It is also possible to carry out a step of maturing of the catalyst,before or after removing the excess of solvent, at ambient temperatureor in the presence of gentle heating, which can range up to 100° C.

In certain embodiments, this maturing can be carried out for a period oftime ranging from 0.1 to 100 hours, advantageously from 0.2 to 20 hours,more advantageously from 1 to 10 hours.

Generally, the second step must be carried out under conditions whichmake possible the deposition, at the surface of the catalyst, of asufficient amount of additive of formula (I), so as to obtain asatisfactory level of activity.

Preferably, at the end of the second step, the total amount ofadditive(s) of formula (I) deposited at the surface of the catalyst,expressed as being the ratio of the molar amount of additive(s) offormula (I) to the total molar amount of metals from Groups VIII andVIB, is at least 0.01 mol of additive(s) per mole of metals from GroupsVIII and VIB. Preferably, this amount is between 0.01 and 10 mol ofadditive(s) per mole of metals from Groups VIII and VIB, more preferablybetween 0.05 and 5 mol and more preferably still between 0.1 and 1.5mol.

During the second step, it is also possible to deposit, in addition tothe additive(s) of formula (I), one or more additional organic orinorganic additives, either simultaneously with the deposition of theadditive(s) of formula (I) or before and/or after the deposition of theadditive(s) of formula (I). Such an additional deposition should,however, be carried out under conditions such that that it does notprejudice the deposition of the additive of formula (I) or its activity.

The regeneration process according to the invention can, in addition tothe two steps described above, optionally comprise one or moreadditional steps carried out before and/or after the said first andsecond steps or also intercalated between these two steps.

Thus, the process according to the invention can advantageouslycomprise, before the said first step, a step of removal of the freeimpurities and hydrocarbons included in the catalyst.

This step can be carried out by washing the catalyst. Such a washing canbe carried out using an appropriate solvent, such as, for example,toluene, xylenes, acetone or any other appropriate solvent.

This step can also advantageously be carried out by stripping using astream of gas, for example air, steam, carbon dioxide or an inert gas,such as nitrogen, at a temperature, for example, of between 100 and 450°C.

The process according to the invention can also comprise, after the saidsecond step, a step of drying the catalyst which can be carried out at atemperature ranging from 80° C. to 350° C., preferably from 100° C. to200° C., in the open air or in the presence of a gas stream of air, ofan inert gas, such as nitrogen, or of any other appropriate gas.

The process according to the invention can also optionally comprise,after the said second step, a step of calcination of the catalyst whichcan be carried out at a temperature ranging from 300° C. to 500° C., inthe open air or in the presence of a gas stream of air, of an inert gas,such as nitrogen, or of any other appropriate gas.

When the process according to the invention already comprises a step ofdrying the catalyst, the calcination step (if one is present) is thencarried out after the drying step.

In certain embodiments, at the end of the process according to theinvention and before any step of conventional sulphurization, the amountof sulphur present at the surface of the catalyst ranges from 0.5 to 8%by weight, preferably from 1 to 5% by weight, with respect to the totalweight of the catalyst. More preferably, the amount of sulphur presentat the surface of the catalyst ranges from 2 to 3% by weight, withrespect to the total weight of the catalyst.

At the end of the process according to the invention, immediately beforethe use of the recycled catalyst, it is advantageous to carry out afinal conventional sulphurization by bringing the catalyst into contactwith one or more sulphurizing agents. This sulphurization can bepreceded or accompanied by an activation in the presence of hydrogen.

The corresponding sulphurizing agents are conventional compounds chosen,for example, from hydrogen sulphide, elemental sulphur, CS₂, organicsulphur compounds, such as mercaptans, sulphides, disulphides orpolysulphides, or hydrocarbon fractions naturally comprising sulphurcompounds and/or enriched in sulphur compounds.

However, according to the present invention, the duration and/or theintensity of the sulphurization can be substantially reduced, incomparison with the processes of the prior art, since the catalyst isprovided in a form which is already presulphurized. This results in asaving in time and in a saving in sulphurizing agents, which are for themost part aggressive and polluting compounds.

When the regenerated catalyst is employed in a process for the treatmentof a hydrocarbon feedstock comprising sulphur compounds, it can also bepossible to carry out the step of activation of the catalyst directlywith the feedstock without adding sulphur compounds thereto, relyingonly on the sulphur present in the feedstock to complete thesulphurization of the catalyst at the necessary stoichiometry. Thisconstitutes a particularly advantageous embodiment of the invention.

The process according to the present invention can be carried out insitu, that is to say directly in the unit in which the catalyst isemployed.

According to a preferred embodiment, it is carried out ex situ, that isto say after discharging the catalyst from the unit.

The process according to the invention can also comprise some stepscarried out in situ, the others being carried out ex situ.

The process according to the present invention makes it possible toregenerate any spent catalyst for the hydrotreating and/orhydroconversion of hydrocarbons in the refining and petrochemistryfields.

They are catalysts comprising at least one metal from Group VIII of thePeriodic Table of the Elements, such as, for example, cobalt, nickel,iron, platinum or palladium, in combination with at least one metal fromGroup VIB, such as, for example, molybdenum, tungsten or chromium. Thecontent of metal or metals from Group VIII is generally between 0.1 and10% by weight, with respect to the total weight of the catalyst, and thecontent of metal or metals from group VIB is generally between 1 and 20%by weight, with respect to the total weight of the catalyst.

These metals are deposited on a support based on one or more refractoryinorganic oxides, such as, in particular, aluminas, silicas,silica/aluminas, zeolites, zirconias, titanium and boron oxides, andmixtures of such oxides.

The process according to the invention is particularly appropriate forthe regeneration of catalysts comprising CoMo, NiMo, NiW or NiCoMo metalcombinations deposited on alumina-based supports.

The spent catalysts may comprise, or may have comprised, in the freshstate or as a consequence of a preceding recycling, one or moreadditives, such as organic additives, halogen compounds, boron compoundsor phosphorus compounds.

The catalysts involved in the process according to the invention aregenerally provided in the form of small solid particles, such as beads,more or less cylindrical particles, or extrudates. They exhibit aspecific surface, measured by the BET method, generally between 100 and300 m²/g, a pore volume, determined by nitrogen adsorption, ranging from0.25 to 1 ml/g and a mean pore diameter, determined by nitrogenadsorption, ranging from 7 to 20 nm.

The present invention also relates to the regenerated catalysts obtainedby means of the process described above. These catalysts exhibit aparticularly satisfactory level of activity and exhibit the additionaladvantage of being presulphurized, as has been explained above.

Another subject-matter of the present invention is the use of one ormore additive(s) of formula (I) as described above in order to increasethe activity of a catalyst comprising at least one metal from Group VIIIand at least one metal from Group VIB which are deposited on arefractory oxide support.

The catalyst involved in this use can be a fresh catalyst or a spentcatalyst which has been regenerated beforehand by at least partialremoval of the coke.

The examples which follow are given purely by way of illustration of thepresent invention.

EXAMPLES Example 1

This example was carried out starting from a spent commercial catalystcomprising 23.1% by weight of MoO₃, 4.2% by weight of CoO, 12.4% byweight of carbon and 14.5% by weight of sulphur.

A portion of this spent catalyst was subjected to a heat treatment at atemperature of 400° C. under air for a period of time of 2 hours, inorder to obtain the treated catalyst T1.

The procedure consists in placing 100 g (equivalent dry weight) ofcatalyst in 5 glass crucibles, in introducing the latter into a mufflefurnace preheated to 300° C., in remaining at this temperature for 1hour, in bringing the furnace to 400° C. and in remaining at thistemperature for 2 hours.

An identical portion of this same spent catalyst was subjected to a heattreatment according to the same procedure but with a temperature of 520°C. for a period of time of 2 hours for the final stationary phase, inorder to obtain the treated catalyst T2.

The characteristics of the catalysts T1 and T2 appear in the tablebelow:

T1 T2 Carbon content (% by weight) 1.3 0.2 Sulphur content (% by weight)0.4 0.2 Specific surface (m²/g) 175 181

100 g of the catalyst T1 were impregnated to saturation of the porevolume with a solution composed of 10 g of polyethylene glycol 200(PEG-200) and of 33 g of demineralized water.

After impregnation, the sample was subjected to a step of maturing at atemperature of 70° C. for 8 hours and then dried under nitrogen in anoven at 140° C. in order to obtain the comparative regenerated catalystA1.

100 g of the catalyst T1 were impregnated to saturation of the porevolume with a solution composed of 14.2 g of a commercial 88% by weightsolution of 2-hydroxy-4-methylthiobutanoic acid (i.e., 12.5 g of2-hydroxy-4-methylthiobutanoic acid) and of 36 g of demineralized water.

After impregnation, the sample was subjected to a step of maturing at atemperature of 70° C. for 8 hours and then dried under nitrogen in anoven at 140° C. in order to obtain the regenerated catalyst according tothe invention A2. This catalyst comprises 4.2% by weight of carbon and2.3% by weight of sulphur.

100 g of the catalyst T2 were impregnated to saturation of the porevolume with a solution composed of 14.2 g of a commercial 88% by weightsolution of 2-hydroxy-4-methylthiobutanoic acid (i.e., 12.5 g of2-hydroxy-4-methylthiobutanoic acid) and of 36 g of demineralized water.

After impregnation, the sample was subjected to a step of maturing at atemperature of 70° C. for 8 hours and then dried under nitrogen in anoven at 140° C. in order to obtain the regenerated catalyst according tothe invention A3. This catalyst comprises 4.4% by weight of carbon and2.4% by weight of sulphur.

The activities of the catalysts T1 and T2 and A1 to A3 in thehydrodesulphurization of hydrocarbons were then compared, the protocoldescribed below being followed.

The feedstock used is a straight run gas oil which exhibits thefollowing characteristics:

Sulphur content (ppm by weight) 12 200 Nitrogen content (ppm by weight)   94 Density (g/ml)    0.837

For each sample, the volume of catalyst employed for the test was 10 ml.

Before the hydrodesulphurization test, each catalyst sample wasactivated by sulphurization after a period of wetting for 3 hours atambient temperature with gas oil additivated with 2.5% by weight ofsulphur using dimethyl disulphide (DMDS). The sulphurization process wascarried out with an hourly space velocity (HSV) of 3 h⁻¹, with anH₂/additivated gas oil ratio of 200 (Sl/h)/(1/h) and a total pressure of3 MPa (30 bar). A first temperature gradient from ambient temperature to250° C. was performed with a gradient of 30° C./h, followed by astationary phase of 8 h at 250° C. A second temperature gradient from250° C. to 320° C. was subsequently performed with a gradient of 20°C./h, followed by a stationary phase of 5 h at 320° C.

The test feedstock was then injected in order to initiate the test. Thetest conditions were as follows: pressure of 3 MPa, H₂/gas oil ratio of300, HSV=2 h⁻¹, temperature from 340 to 350° C.

The sulphur content of the feedstock was measured at the outlet of theunit using a UV fluorescence analyser. The apparent constants of thedesulphurization reaction were calculated according to the followingformula E1:

$\begin{matrix}{K_{v} = {\left( \frac{1}{\alpha - 1} \right)\left( {\frac{1}{S^{\alpha - 1}} - \frac{1}{S_{0}^{\alpha - 1}}} \right)*{HSV}}} & ({E1})\end{matrix}$

with

K_(v)=apparent reaction constant

α=order of reaction (regarded as equal to 1.2)

S=sulphur content of the effluents

S₀=sulphur content of the feedstock

HSV=hourly space velocity of the liquid feedstock

The performance of each sample was evaluated with respect to that of areference catalyst. For this, the relative volume activity (RVA) wascalculated according to the following formula E2:

$\begin{matrix}{{RVA} = {\frac{{Kv}({sample})}{{Kv}({reference})} \times 100}} & ({E2})\end{matrix}$

The K_(v) value of 100 was assigned to the treated catalyst T2 asreference.

The results obtained are collated in the table below:

Temperature of RVA Catalyst the heat treatment Additive (%) Treatedcatalyst T1 400° C. No 106 Treated catalyst T2 520° C. No 100Comparative 400° C. PEG-200 129 regenerated catalyst A1 Regenerated 400°C. 2-Hydroxy-4- 142 catalyst according to methylthiobutanoic theinvention A2 acid Regenerated 520° C. 2-Hydroxy-4- 155 catalystaccording to methylthiobutanoic the invention A3 acid

The results which appear in the above table show that the catalysts A2and A3, regenerated by means of a process according to the invention,are more active than the treated catalysts T1 and

T2 and than the comparative regenerated catalyst A1.

Example 2

The regenerated catalysts A4 and A5 according to the invention wereprepared in an identical manner to the respective catalysts A2 and A3 ofExample 1 above but while doubling the amount of additive(2-hydroxy-4-methylthiobutanoic acid) employed during the second step,so as to increase the sulphur content of the regenerated catalyst(pre-sulphurization):

100 g of the catalyst T1 were impregnated to saturation of the porevolume with a solution composed of 28.4 g of a commercial 88% by weightsolution of 2-hydroxy-4-methylthiobutanoic acid (i.e., 25 g of2-hydroxy-4-methylthiobutanoic acid) and of 24.5 g of demineralizedwater.

After impregnation, the sample was subjected to a step of maturing at atemperature of 70° C. for 8 hours and then dried under nitrogen in anoven at 140° C. in order to obtain the regenerated catalyst according tothe invention A4. This catalyst comprises 8.2% by weight of carbon and4.3% by weight of sulphur.

100 g of the catalyst T2 were impregnated to saturation of the porevolume with a solution composed of 28.4 g of a commercial 88% by weightsolution of 2-hydroxy-4-methylthiobutanoic acid (i.e., 25 g of2-hydroxy-4-methylthiobutanoic acid) and of 24.5 g of demineralizedwater.

After impregnation, the sample was subjected to a step of maturing at atemperature of 70° C. for 8 hours and then dried under nitrogen in anoven at 140° C. in order to obtain the regenerated catalyst according tothe invention A5. This catalyst comprises 8.1% by weight of carbon and4.5% by weight of sulphur.

The activities of the catalysts A4 and A5 in the hydrodesulphurizationof hydrocarbons were then tested, a protocol identical to that describedin Example 1 above being followed, with the exception of the treatmentfor activation by sulphurization, which is carried out with the same gasoil as in Example 1 but not additivated with DMDS. As for the rest, thesulphurization procedure remains absolutely identical to that of Example1, and also the hydrodesulphurization test in itself.

The results obtained are collated in the following table:

Temperature of RVA Catalyst the heat treatment Additive (%) Regenerated400° C. 2-Hydroxy-4- 139 catalyst according to methylthiobutanoic theinvention A4 acid Regenerated 520° C. 2-Hydroxy-4- 150 catalystaccording to methylthiobutanoic the invention A5 acid

The results which appear in the above table show that the catalysts A4and A5, regenerated by means of the process according to the inventionwhile employing a greater amount of 2-hydroxy-4-methylthiobutanoic acid,exhibit an activity comparable to that of the catalysts A2 and A3 andgreater than that of the comparative catalyst A1.

Thus, the process according to the invention makes it possible toprepare catalysts, the activation of which does not require the use ofspecific sulphurizing agents but can, in contrast, be carried outdirectly with the gas oil to be desulphurized.

INCORPORATION BY REFERENCE

The contents of all references (including literature references, issuedpatents, published patent applications, and co-pending patentapplications) cited throughout this application are hereby expresslyincorporated herein in their entireties by reference.

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents of the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims.

1. A process for the regeneration of a catalyst comprising at least onemetal from Group VIII and at least one metal from Group VIB which aredeposited on a refractory oxide support, comprising: at least one firststep of heat treatment of the catalyst in the presence of oxygen and ata temperature ranging from 350° C. to 550° C.; at least one second stepof deposition, at the surface of the catalyst, of one or moreadditive(s) of formula (I):

in which: R₁ denotes a hydrogen atom or a saturated or unsaturated,linear or branched hydrocarbon group comprising from 1 to 30 carbonatoms; R₂ denotes a saturated or unsaturated, linear or brancheddivalent hydrocarbon group comprising from 1 to 30 carbon atoms whichcan optionally comprise one or more heteroatom(s) chosen from oxygen andnitrogen atoms; R₃ denotes a saturated or unsaturated, linear orbranched hydrocarbon group comprising from 1 to 30 carbon atoms.
 2. Theprocess according to claim 1, characterized in that the said first stepis carried out at a temperature of less than or equal to 530° C.
 3. Theprocess according to claim 1, characterized in that the said first stepis carried out, in all or in part, at a temperature of greater than 500°C. and less than or equal to 550° C.
 4. The process according to claim1, characterized in that, in the formula (I), R₁ denotes a hydrogen atomor a saturated or unsaturated, linear or branched hydrocarbon groupcomprising from 1 to 8 carbon atoms and preferably from 1 to 4 carbonatoms.
 5. The process according to claim 1, characterized in that, inthe formula (I), R₂ denotes a saturated or unsaturated, linear orbranched divalent hydrocarbon group comprising from 1 to 8 carbon atoms,preferably from 1 to 6 carbon atoms, which can be substituted by one ormore —OH, —OR, —NH₂, —NHR or —NRR′ groups, with R and R′ denoting alkylgroups comprising from 1 to 4 carbon atoms and preferably 1 or 2 carbonatoms.
 6. The process according to claim 1, characterized in that, inthe formula (I), R₃ denotes a saturated or unsaturated, linear orbranched hydrocarbon group comprising from 1 to 8 carbon atoms andadvantageously from 1 to 4 carbon atoms.
 7. The process according toclaim 6, wherein in the saturated or unsaturated, linear or branchedhydrocarbon group comprises from 1 to 4 carbon atoms.
 8. The processaccording to claim 1, characterized in that the additive of formula (I)is 2-hydroxy-4-methylthiobutanoic acid.
 9. The process according toclaim 1, characterized in that the additive or additives of formula (I)is (are) deposited on the catalyst by impregnation with one or moreaqueous solution(s) of the (of these) additive(s).
 10. The processaccording to claim 1, characterized in that, at the end of the saidsecond step, the total amount of additive(s) of formula (I) deposited atthe surface of the catalyst, expressed as the ratio of the molar amountof additive(s) of formula (I) to the total molar amount of metals fromGroups VIII and VIB, is at least 0.01 mol of additive(s) per mole ofmetals from Groups VIII and VIB.
 11. The process according to claim 10,characterized in that, at the end of the said second step, the totalamount of additive(s) of formula (I) deposited at the surface of thecatalyst is between 0.01 and 10 mol of additive(s) per mole of metalsfrom Groups VIII and VIB.
 12. The process according to claim 1,characterized in that it comprises one or more additional steps carriedout before and/or after the said first and second steps or alsointercalated between these two steps.
 13. The process according to claim12, characterized in that it comprises, before the said first step, astep of removal of the free impurities and hydrocarbons by washing thecatalyst with a solvent or by stripping using a stream of gas.
 14. Theprocess according to claim 12, characterized in that it comprises, afterthe said second step, a step of drying the catalyst, carried out at atemperature ranging from 80° C. to 350° C., in the open air or in thepresence of a gas stream of air, of an inert gas, such as nitrogen, orof any other appropriate gas.
 15. The process according to claim 1,characterized in that it is carried out ex situ, that is to say afterdischarging the catalyst from the unit.
 16. The process according toclaim 1, characterized in that, at the end of this process and beforeany step of sulphurization proper, the amount of sulphur present at thesurface of the catalyst ranges from 0.5 to 8% by weight, advantageouslyfrom 1 to 5% by weight, with respect to the total weight of thecatalyst.
 17. The process according to claim 16, wherein the amount ofsulphur present at the surface of the catalyst ranges from 1 to 5% byweight
 18. A regenerated catalyst obtained the process according toclaim
 1. 19. A method to increase the activity of a catalyst comprisingat least one metal from Group VIII and at least one metal from Group VIBwhich are deposited on a refractory oxide support, comprising contactingsaid catalyst with one or more additive(s) of formula (I):

in which: R₁ denotes a hydrogen atom or a saturated or unsaturated,linear or branched hydrocarbon group comprising from 1 to 30 carbonatoms; R₂ denotes a saturated or unsaturated, linear or brancheddivalent hydrocarbon group comprising from 1 to 30 carbon atoms whichcan optionally comprise one or more heteroatom(s) chosen from oxygen andnitrogen atoms; R₃ denotes a saturated or unsaturated, linear orbranched hydrocarbon group comprising from 1 to 30 carbon atoms, therebyincreasing the activity of said catalyst.